A dry smelting method for producing a nickel mat by using a smelting furnace, a dry smelting method for producing ferronickel that is an alloy of iron and nickel by using a rotary kiln or a movable hearth furnace, a wet smelting method for producing mixed sulfide by using an autoclave, and the like are known as a method for smelting a nickel oxide ore referred to as limonite or saprolite that is one type of oxide ore.
In various methods described above, in particular, in a case where the nickel oxide ore is reduced and smelted by using the dry smelting method, in order to advance a reaction, a treatment of forming a lump product by crushing the nickel oxide ore that is a raw material to have a suitable size is performed as a pretreatment.
Specifically, when a nickel oxide ore is formed into a lump product, that is, a powder-like ore or a fine-grained ore is formed into a lump-like ore, it is general that the nickel oxide ore, and other components, for example, a binder and a reducing agent such as a coke are mixed to be a mixture, the mixture is subjected to moisture adjustment or the like, and then, is put into a lump product producing machine, and for example, a lump product of which one side or a diameter is approximately 10 mm˜30 mm (indicating a pellet, a briquette, and the like, and hereinafter, will be simply referred to as a “pellet”).
It is necessary that the pellet obtained by being formed into the lump product has a certain degree of aeration properties in order to “drain” the contained moisture. Further, in the subsequent reduction treatment, in a case where the reduction is not homogeneously advanced in the pellet, the composition of a reduced product to be obtained is inhomogeneous, and a problem that a metal is dispersed or unevenly distributed occurs. For this reason, it is important to homogeneously mix the mixture at the time of preparing the pellet, or to maintain a homogeneous temperature to a maximum extent at the time of reducing the obtained pellet.
In addition, coarsening a metal (ferronickel) that is generated by the reduction treatment is also an extremely important technology. In a case where ferronickel that is generated, for example, has a fine size of several tens of μm to several hundreds of μm, it is difficult to separate ferronickel from a slag that is simultaneously generated, and a recovery rate (a yield) as ferronickel greatly decreases. For this reason, a treatment for coarsening ferronickel after the reduction is necessary.
In addition, it is also an important technical matter how a smelting cost can be suppressed to be low, and a continuous treatment that can be operated in a compact facility is desirable.
For example, in Patent Document 1, a method for producing a granular metal of supplying an agglomerated product containing a metal oxide and a carbonaceous reducing agent onto a hearth of a moving bed type reduction melting furnace, of performing heating, and performing reduction melting with respect to the metal oxide, in which when a relative value of a projected area ratio of a hearth of an agglomerated product with respect to a maximum projected area ratio of a hearth of an agglomerated product at the time of setting a distance between the agglomerated products to 0 is set to a base density, an agglomerated product having an average diameter of 19.5 mm˜32 mm is supplied onto the hearth such that the base density is 0.5˜0.8, and is heated, is disclosed. In Patent Document 1, it is described that it is possible to increase the productivity of granular metal iron by controlling the base density and the average diameter of the agglomerated product together, in the method.
However, the method disclosed in Patent Document 1 is a technology for controlling a reaction occurring outside the agglomerated product, and does not focus on the control of a reaction occurring in the agglomerated product which is the most important factor in the reduction reaction. On the other hand, it is required to increase a reaction efficiency by controlling the reaction occurring in the agglomerated product, and to obtain a higher quality metal (a metal and an alloy) by more homogeneously advancing the reduction reaction.
In addition, as with Patent Document 1, in a method using an agglomerated product having a specific diameter as the agglomerated product, it is necessary to remove an agglomerated product not having a specific diameter, and thus, a yield at the time of preparing the agglomerated product decreases. In addition, in the method of Patent Document 1, it is necessary to adjust the base density of the agglomerated product to be 0.5˜0.8, and it is not possible to laminate the agglomerated product, and thus, the productivity is low. As described above, in the method in Patent Document 1, a production cost is high.
Further, as with Patent Document 1, in a process using a so-called total melting method in which all raw materials are melted and reduced, there is a major problem on an operation cost. For example, in order to completely melt a nickel oxide ore that is a raw material, a high temperature of 1500° C. or higher is necessary, but a considerable energy cost is required for such a high temperature condition, and a furnace that is used at such a high temperature is easily damaged, and thus, a repair cost is also required. Further, only approximately 1% of nickel is contained in the nickel oxide ore that is the raw material, and thus, even though it is not necessary to recovery other than iron corresponding to nickel, all components that are contained in large amounts and are not required to be recovered are melted, which is extremely inefficient.
Therefore, a reduction method of partial melting has been considered in which only necessary nickel is reduced, but iron that is contained in larger amounts than nickel is partially reduced. However, in such a partial reduction method (or also referred to as a nickel preferential reduction method), a reduction reaction is performed while a raw material is maintained in a semi-solid state where the raw material is not completely melted, and thus, it is not easy to control the reaction such that the reduction of iron is within a range corresponding to nickel while 100% of nickel is completely reduced. Accordingly, there is a problem that a partial variation in the reduction of the raw material occurs, and efficient operation is difficult due to a decrease in a nickel recovery rate.
As described above, in a technology of producing a metal or an alloy by mixing and reducing an oxide ore, there are many problems in increasing the productivity or the efficiency, reducing the production cost, and increasing the quality of the metal by homogeneously advancing the reduction reaction.    Patent Document 1: Japanese Unexamined Patent Application, Publication No. 2011-256414